This application is based on and incorporates herein by reference Japanese Patent Application Nos. 2000-308123 filed on Oct. 6, 2000, and 2001-172450 filed on Jun. 7, 2001.
1. Field of the Invention
The present invention relates to a valve timing adjusting device for changing a valve timing of at least one of an intake valve and an exhaust valve in an internal combustion engine.
2. Description of the Prior Art
Conventionally, there has been known a vane type valve timing adjusting device in which a camshaft is driven through a timing pulley or a chain sprocket adapted to rotate synchronously with a crankshaft of an engine and the valve timing of one of an intake valve and an exhaust valve is controlled hydraulically in accordance with a phase difference based on a relative rotation between the timing pulley or the chain sprocket and the camshaft.
JP-A-1-92504 discloses a valve timing adjusting device in which a relative rotation between a driving shaft system such as a timing pulley or a chain sprocket and a driven shaft system such as a camshaft is restrained when both systems are each in a predetermined relative rotational position. According to the valve timing adjusting device disclosed in JP-A-1-92504, when a vane in the driven shaft system is in a predetermined relative rotational position with respect to a rotor in the drive shaft system, a knock pin provided on the vane side is allowed to enter one of two holes formed in the rotor to restrain a relative rotation between the rotor and the vane. However, in the valve timing adjusting device, if an appropriate clearance is not present between each of the two holes formed in the rotor and the knock pin, the knock pin will be unable to fit in the holes or a striking sound may occur upon fitting of the two. There also is the problem that the clearance between one of the holes and the knock pin may become larger little by little due to a friction between the hole and the knock pin.
U.S. Pat. No. 5,23,152 discloses a valve timing adjusting device to solve the problem. According to the device disclosed therein, a fitting portion between a stopper piston corresponding to the above knock pin and a stopper hole is formed as a tapered portion to ensure a strong restraining force induced by the resulting wedge effect. The occurrence of a striking sound upon fitting of the stopper piston and the stopper hole is prevented, and a change of a relative rotation restraining position which is attributable to a change or variations in the clearance between the stopper piston and the stopper hole is prevented.
However, according to the device disclosed in the U.S. Pat. No. 5,823,152, a vane provided with the stopper piston and a housing provided with the stopper hole are restrained by abutment of slant faces not perpendicular to a direction in which the vane rotates relatively with respect to the housing. Thus, the stopper piston may slip off the stopper hole, thereby making it impossible to restrain a relative rotation between a timing pulley or a chain sprocket and a camshaft, if a large disturbance factor acts on a contact portion between the stopper piston and a wall surface of the stopper hole or if a frictional coefficient of the contact portion becomes extremely small.
An object of the present invention to provide a valve timing adjusting device capable of restraining a relative rotation between a driving shaft system and a driven shaft system at a predetermined angular position, and capable of suppressing the occurrence of a striking sound at the time of restraining the relative rotation between both systems.
According to a first aspect of the present invention, a hole for retaining a restraining pin is formed by a straight hole having an axis perpendicular to the direction of a relative rotation of a vane member with respect to a housing member, and a tapered hole which is formed on a deep side of the straight hole and which is reduced in diameter on a deep side thereof.
With a wedge effect induced by the tapered hole and the restraining pin, it is possible to restrain a relative rotation between the driving shaft system and the driven shaft system at a predetermined angular position and suppress the occurrence of a striking noise. Even if the restraining pin is retreated from the tapered hole under the influence of a disturbance or a lowering of the frictional coefficient, the restraining pin can be retained in straight hole with a vertical drag exerted by a wall surface of the straight hole on an outer wall surface of the restraining pin, so that a relative rotation between the driving shaft system and the driven shaft system can be restrained in a predetermined angular range.
According to a second aspect of the present invention, a restraining pin, which is advanced into a straight hole having an axis perpendicular to the direction of a relative rotation of a vane member with respect to a housing member, is formed with a first cylindrical portion and a second cylindrical portion different in thickness from each other. A relative rotation of the vane member with respect to the housing member is sure to be restrained in stages. More specifically, a relative rotation of the vane member with respect to the housing member is restrained in a predetermined angular range by advancing the first cylindrical portion smaller in diameter than the second cylindrical portion into the straight hole. Thus, while the vane member rotates relatively with respect to the housing member in the angular range due to a change in load imposed on the driven shaft, the second cylindrical portion larger in diameter than the first cylindrical portion can be easily advanced into the straight hole. Therefore, as the first stage, a phase difference in a predetermined range can surely be set between the driving system and the driven system in a somewhat allowed state of the relative rotation of the vane member with respect to the housing member. As the second stage, a target phase difference can be set between the driving system and the driven system, and it is also possible to set small a clearance between the second cylindrical portion and the straight hole to suppress the occurrence of a striking sound. Moreover, even in the event a large disturbance factor acts on the contact portion between the restraining pin and the straight hole wall surface or even if the frictional coefficient of the contact portion is extremely small, a phase difference can be controlled because the restraining pin is retained in the straight hole with a drag which the straight hole wall surface exerts on the first and second cylindrical portions.
According to a third aspect of the present invention, a restraining pin, which is advanced into a hole having an axis perpendicular to the direction of a relative rotation of a vane member with respect to a housing member, is formed with a front end portion and a base end portion different in thickness from each other. A stepped outer wall surface is formed by outer walls of the front end portion and the base end portion, whereby the relative rotation of the vane member with respect to the housing member is sure to be restrained. More specifically, a relative rotation of the vane member with respect to the housing member is restrained in a predetermined angular range by advancing the front end portion smaller in diameter than the base end portion into the hole, then while the vane member rotates relatively with respect to the housing member in the angular range due to a change in load imposed on the driven shaft, the base end portion larger in diameter than the front end portion can be easily advanced into the hole. Therefore, as the first stage, a phase difference in a predetermined range can surely be set between the driving system and the driven system in a somewhat allowed state of the relative rotation of the vane member with respect to the housing member. As the second stage, a target phase difference can be set between the driving system and the driven system and it is also possible to set small a clearance between the base end portion and the hole to suppress the occurrence of a striking sound. Besides, by utilizing the difference in diameter, the clearance between the front end portion of the pin and the hole can be set large to permit easy advance of the front end portion into the hole. Moreover, since a stepped portion is provided between the front end portion and the base end portion of the restraining pin, the depth of insertion of the restraining pin into the hole at the time of restraining the relative rotation of the vane member with respective to the housing member in the predetermined angular range and the depth of insertion of the restraining pin into the hole at the time of restraining the relative rotation of the vane member with respect to the housing member to a predetermined angular position are difficult to be changed by variations in manufacture.